<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    var maximumUnits = function (boxTypes, truckSize) {
      boxTypes.sort((a, b) => b[1] - a[1]);
      let ans = 0;
      for (let [count, size] of boxTypes) {
        if (truckSize > count) {
          ans += size * count;
          truckSize -= count;
        } else {
          ans += truckSize * size;
          break;
        }
      }
      return ans;
    }
    console.log(maximumUnits([[1, 3], [2, 2], [3, 1]], 4))
  </script>
</body>

</html>